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Apollo-Simulation-Peripheral-Lab / DSKY

An affordable and easy to manufacture DSKY replica
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Consistency issues with few LEDs and low duty cycle #20

Closed Aeasala closed 6 months ago

Aeasala commented 6 months ago

The apparent brightness of the LEDs is significantly greater at low duty cycles, and few powered. (1-2 LEDs)

Ruled out:

This may be due to drain-source capacitance on the PWM FET, not having enough time to completely charge with only 1 LED active during the OFF state. (LED FET is still turned on while capacitance charges.)

Aeasala commented 6 months ago

As other pins have a shared pulldown, this is due to the lack of a hi-z output state. LOW pins begin to sink current from HIGH pins, causing a stronger drive. Hard to explain, but some isolation will be needed.

Aeasala commented 6 months ago

Pulldowns may/may not become DNP depending on I/O expander behavior.

Aeasala commented 6 months ago

PU PD omitted.